The blaze broke out on the 1100 block of Hamilton Street around 5:30 p.m., said firefighters. Crews were still on the scene as late as 10:30 p.m., according to city fire officials.
Photos from the scene showed heavy smoke and visible flames from a row building block containing apartments and businesses on the ground floor.
Twenty-one people were assisted by the American Red Cross, the organization said.
"Thank you to our volunteers who responded to the scene and the rest of our team who is supporting the families affected by this fire," said the Red Cross of Greater Pennsylvania.
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